E-arşiv Çankayahttp://earsiv.cankaya.edu.tr:8080/xmlui
DSpace dijital arşiv sistemi toplar, depolar, dizinler, korur ve dijital araştırma materyallerini dağıtmaya aracılık eder.Tue, 26 Sep 2017 21:40:46 GMT2017-09-26T21:40:46ZPooling through lateral transshipments in service parts systemshttp://hdl.handle.net/123456789/1631
Pooling through lateral transshipments in service parts systems
Satır, Benhür; Savasaneril, Seçil; Serin, Yasemin
We study the inventory management problem of a service center operating in a decentralized service parts network. The service centers collaborate through inventory and service pooling, and through sharing information on the inventory status. Upon demand arrival, a service center may request a part from the other center, in which case a payment is made. Under this competitive and collaborative environment, we first characterize the optimal operating policy of an individual service center. Through computational analysis we identify the conditions under which pooling is most beneficial to the service center, and make an assessment of different pooling strategies which are commonly adopted in practice and in the literature. Finally, we analyze the effect of interaction between the centers on the benefit of pooling
Mon, 16 Jul 2012 00:00:00 GMThttp://hdl.handle.net/123456789/16312012-07-16T00:00:00ZA decision support system for locating weapon and radar positions in stationary point air defencehttp://hdl.handle.net/123456789/1630
A decision support system for locating weapon and radar positions in stationary point air defence
Tanergüçlü, Türker; Maras, Hakan; Gencer, Cevriye; Aygüneş, Haluk
In this study, a decision support system (DSS) based on the interactive use of location models and geographical information systems (GIS) was developed to determine the optimal positions for air defence weapons and radars. In the location model, the fire units are considered as the facilities to be located and the possible approach routes of air vehicles are treated as demand points. Considering the probability that fire by the units will miss the targets, the objective of the problem is to determine the positions that provide coverage of the approach routes of the maximum number of weapons while considering the military principles regarding the tactical use and deployment of units. In comparison with the conventional method, the proposed methodology presents a more reliable, faster, and more efficient solution. On the other hand, owing to the DSS, a battery commander who is responsible for air defence becomes capable of determining the optimal weapon and radar positions, among the alternative ones he has identified, that cover the possible approach routes maximally. Additionally, he attains the capability of making such decisions in a very short time without going to the field over which he will perform the defence and hence without being subject to enemy threats. In the decision support system, the digital elevation model is analysed using Map Objects 2.0, the mathematical model is solved using LINGO 4.0 optimization software, and the user interface and data transfer are supported by Visual Basic 6.0.
Sun, 01 Apr 2012 00:00:00 GMThttp://hdl.handle.net/123456789/16302012-04-01T00:00:00ZMulti-item two-echelon spare parts inventory control problem with batch ordering in the central warehouse under compound Poisson demandhttp://hdl.handle.net/123456789/1629
Multi-item two-echelon spare parts inventory control problem with batch ordering in the central warehouse under compound Poisson demand
Topan, Engin; Bayındır, Z.P.
We consider a multi-item two-echelon spare part inventory system in which the central warehouse operates under an (nQ, R) policy and the local warehouses implement order-up-to S policy, each facing a compound Poisson demand. The objective is to find the policy parameters minimizing expected system-wide inventory holding and fixed ordering costs subject to an aggregate mean response time constraint at each warehouse. In this paper, we propose four alternative approximations for the steady state performance of the system; and extend a heuristic and a lower bound proposed under Poisson demand assumption to the compound Poisson setting. In a computational study, we show that the performances of the approximations, the heuristic, and the lower bound are quite satisfactory; and the relative cost saving of setting an aggregate service level rather than individually for each part is quite high
Wed, 01 Aug 2012 00:00:00 GMThttp://hdl.handle.net/123456789/16292012-08-01T00:00:00ZInference in multivariate linear regression models with elliptically distributed errorshttp://hdl.handle.net/123456789/1628
Inference in multivariate linear regression models with elliptically distributed errors
Islam, M. Qamarul; Yıldırım, Fetih; Yazıcı, Mehmet
In this study we investigate the problem of estimation and testing of hypotheses in multivariate linear regression models when the errors involved are assumed to be non-normally distributed. We consider the class of heavy-tailed distributions for this purpose. Although our method is applicable for any distribution in this class, we take the multivariate t-distribution for illustration. This distribution has applications in many fields of applied research such as Economics, Business, and Finance. For estimation purpose, we use the modified maximum likelihood method in order to get the so-called modified maximum likelihood estimates that are obtained in a closed form. We show that these estimates are substantially more efficient than least-square estimates. They are also found to be robust to reasonable deviations from the assumed distribution and also many data anomalies such as the presence of outliers in the sample, etc. We further provide test statistics for testing the relevant hypothesis regarding the regression coefficients
Sun, 03 Aug 2014 00:00:00 GMThttp://hdl.handle.net/123456789/16282014-08-03T00:00:00Z